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Subject: Re: 2.6.39-rc5+ BUG at scsi_run_queue+0x24/0xe3
From: James Bottomley <James.Bottomley@suse.de>
To: Jim Schutt <jaschut@sandia.gov>
Cc: linux-kernel@vger.kernel.org, linux-scsi <linux-scsi@vger.kernel.org>
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	 <1304442019.10982.7.camel@mulgrave.site>  <4DC03B0A.50209@sandia.gov>
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Date: Tue, 03 May 2011 17:37:30 +0000
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On Tue, 2011-05-03 at 11:27 -0600, Jim Schutt wrote:
> James Bottomley wrote:
> > On Tue, 2011-05-03 at 10:53 -0600, Jim Schutt wrote:
> >> Please let me know if what further information you need, or if there is
> >> anything I can do, to help resolve this.
> > 
> > I think this is the fix (already in rc-fixes):
> > 
> > James
> > 
> > ---
> > From 3e85ea868dbd60a84240be5c1eebc36841b9c568 Mon Sep 17 00:00:00 2001
> > From: James Bottomley <James.Bottomley@suse.de>
> > Date: Sun, 1 May 2011 09:42:07 -0500
> > Subject: [PATCH] [SCSI] fix oops in scsi_run_queue()
> > 
> > The recent commit closing the race window in device teardown:
> > 
> > commit 86cbfb5607d4b81b1a993ff689bbd2addd5d3a9b
> > Author: James Bottomley <James.Bottomley@suse.de>
> > Date:   Fri Apr 22 10:39:59 2011 -0500
> > 
> >     [SCSI] put stricter guards on queue dead checks
> > 
> > is causing a potential NULL deref in scsi_run_queue() because the
> > q->queuedata may already be NULL by the time this function is called.
> > Since we shouldn't be running a queue that is being torn down, simply
> > add a NULL check in scsi_run_queue() to forestall this.
> > 
> > Signed-off-by: James Bottomley <James.Bottomley@suse.de>
> > 
> > diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> > index e9901b8..03979f4 100644
> > --- a/drivers/scsi/scsi_lib.c
> > +++ b/drivers/scsi/scsi_lib.c
> > @@ -404,6 +404,10 @@ static void scsi_run_queue(struct request_queue *q)
> >  	LIST_HEAD(starved_list);
> >  	unsigned long flags;
> >  
> > +	/* if the device is dead, sdev will be NULL, so no queue to run */
> > +	if (!sdev)
> > +		return;
> > +
> >  	if (scsi_target(sdev)->single_lun)
> >  		scsi_single_lun_run(sdev);
> >  
> 
> Hmmm, with the above added, I still get BUGs.  Here's an
> example:
> 
> [   17.142931] BUG: unable to handle kernel NULL pointer dereference at           (null)
> [   17.143002] IP: [<ffffffffa01cf8c5>] scsi_run_queue+0x24/0xec [scsi_mod]

Ooh, compiler optimisation, I think; try this instead

James

---

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index e9901b8..0bac91e 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -400,10 +400,15 @@ static inline int scsi_host_is_busy(struct Scsi_Host *shost)
 static void scsi_run_queue(struct request_queue *q)
 {
 	struct scsi_device *sdev = q->queuedata;
-	struct Scsi_Host *shost = sdev->host;
+	struct Scsi_Host *shost;
 	LIST_HEAD(starved_list);
 	unsigned long flags;
 
+	/* if the device is dead, sdev will be NULL, so no queue to run */
+	if (!sdev)
+		return;
+
+	shost = sdev->host;
 	if (scsi_target(sdev)->single_lun)
 		scsi_single_lun_run(sdev);
 



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